This works employs a mechanistic approach that draws upon cell biological, biochemical, and genetic approaches to further our knowledge of the molecular basis for the clinical manifestations of autosomal dominant polycystic liver disease (ADPLD). Polycystic liver disease is characterized by the presence of bile-duct cysts spread throughout the liver parenchyma. It often occurs in association with autosomal dominant polycystic kidney disease (ADPKD), but it also exists as a distinct entity, ADPLD. We have identified two genes mutated in ADPLD:PRKCSH , which encodes the beta-subunit of the ER sugar-processing enzyme glucosidase II (Gllbeta) and SEC63, which encodes SEC63, a component of the ER co-translational protein translocation machinery. Both proteins function in the same pathway of integral membrane and secreted protein's co-translational translocation (SEC63), folding and maturation (PRKCSH). When we conditionally inactivate the PLD genes in the kidney and liver in mice, both bile duct and kidney tubule cysts occur (unlike the human scenario where no kidney phenotype has been reported). These data suggest that PLD genes play a role in cystogenesis as a whole by a cellular recessive mechanism . Based on these observations, we are hypothesizing that the genes causing ADPLD play a role in the biogenesis of ADPKD/ARPKD proteins, namely, polycystin-1 (PC-1, encoded by Pkd1), polycystin-2 (PC-2, encoded by Pkd2) and fibrocystin (FPC, encoded by Pkhd1). These are integral membrane proteins which localize to primary cilia, an organelle whose role in the pathogenesis of cystic diseases of the kidney and liver has recently been unveiled. In the current proposal we wil assess the genetic interaction between Prkcsh/Sec63 and Pkd1/Pkd2/Pkhd1 using mouse models (Aim1) and isolate and characterize murine Prkcsh-/- and Sec63-/- epithelial cell line models and investigate associated cellular abnormalities (Aim 2). For Aim 1, we will cross the Pld1lox/lox/Pld2lox/lox:KspCre(kidney specific Cre) mouse with a Pkd1/Pkd2/Pkhd1 del/del mouse or a mouse containing a low-copy Pkd1BAC/Pkd2BAC transgene and use cyst formation as a readout. We will thus assess whether modulating the copy number of the genes potentially linked with Prkcsh and Sec63 has an effect on the severity of cyst formation. For Aim 2, we will isolate kidney epithelial cell lines containing Prkcsh/Sec63 floxed alleles and induce recombination by Cre transfection. We will then assess whether the biogenesis and trafficking of PC-1, PC-2 or FC is affected on this background. This work is very relevant to public health as it will help achieve a molecular and genetic understanding of ADPLD and provide ways of converting that understanding into strategies for effective therapy.